An estimated one million fish turned up dead in a southern California marina, creating a floating feast for pelicans, gulls and other sea life and a stinky mess for harbour authorities.

The sardines apparently depleted the water of oxygen and suffocated after getting lost in the marina, officials said.

“All indications are it is a naturally occurring event,” said Andrew Hughan, a California Fish and Game spokesman at the scene.

The die-off was unusual but not unprecedented.

“In the world of fishing this is an afternoon’s catch,” he noted.

Boaters awakened to find a carpet of small silvery fish surrounding their vessels, said Staci Gabrielli, marine coordinator for King Harbor Marina on the Los Angeles County coast.

Authorities said there was also a layer of up to 1.5 feet of dead fish on the bottom of the marina.

The scale was impressive to locals at King Harbor, which shelters about 1,400 boats on south Santa Monica Bay.

“The fishermen say they’ve never seen anything this bad that wasn’t red tide,” Mr Hughan said, referring to the natural blooms of toxic algae that can kill fish. Brent Scheiwe, an official of Sea Lab, a Los Angeles Conservation Corps research program at Redondo, said testing of some of the water showed oxygen levels near zero.

Mr Hughan said water samples showed no oils or chemicals that could have contributed to the deaths. He said some of the fish were being shipped to a fish and game laboratory for study, but the cause was likely to be uncomplicated.

The fish appeared to have come into the marina during the night and probably could not find their way out, he said.

“The simplest explanation is the fish got lost. ... They get confused easily,” he said.

Mr Hughan said there was no safety issue at all but “it’s going to smell bad for quite a while.”

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